The future. According to Wired.com please log in to view this image http://www.wired.co.uk/magazine/archive/2013/11/play/manchester-united-upgrade/viewgallery/329938
The best plan IMO is (like mentioned in the article) turning the outside of the stadium into a giant curved screen. People can watch outside "Henman hill" style. They can also be assigned numbers based on a raffle or loyalty system. If Man Utd are losing they can then take the seats of the thousands of supporters leaving before full time. To make things quicker and safer a special exit can be constructed for early leavers called the Glory Tunnel, which leads out to the Glory Hole.
More elbow room for the United glory hunting tourists to watch the games from behind their cameras and ipads?
"fans without tickets" I think it is far more likely you will need a ticket to get into that part of the stadium as well, just not a match ticket maybe